Interventions for loneliness in older adults: a systematic review of reviews

Loneliness in older persons is a major risk factor for adverse health outcomes. Before the COVID-19 pandemic led to unprecedented isolation and hampered programs aimed at preventing or reducing loneliness, many interventions were developed and evaluated. However, previous reviews provide limited or conflicting summaries of intervention effectiveness. This systematic review aimed to assess previous review quality and bias, as well as to summarize key findings into an overarching narrative on intervention efficacy. The authors searched nine electronic databases and indices to identify systematic reviews of interventions to reduce loneliness in older people prior to the COVID-19 pandemic; 6,925 records were found initially. Of these, 19 reviews met inclusion criteria; these encompassed 101 unique primary intervention studies that varied in research design, sample size, intervention setting, and measures of loneliness across 21 nations. While 42% of reviews had minimal risk of bias, only 8% of primary studies appraised similarly. Among the 101 unique articles reviewed, 63% of tested interventions were deemed by article author(s) as effective or partially effective. Generally, interventions that included animals, psychological therapies, and skill-building activities were more successful than interventions focused on social facilitation or health promotion. However, interventions that targeted multiple objectives aimed at reducing loneliness (e.g., improving social skills, enhancing social support, increasing social opportunities, and changing maladaptive social cognition) were more effective than single-objective interventions. Future programs should incorporate multiple approaches, and these interventions should be rigorously tested.


Introduction
Reported prevalence of loneliness among older adults varies widely, with estimates from 7 to 63%, while many reports estimate a point prevalence around 20% (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14).Incidence may be increasing throughout the world (1,(15)(16)(17).Some explanations for the increases in rates of loneliness are associated with increased longevity, greater years lived with disability, and degradation of social support over time (4,(18)(19)(20)(21).An increase in single living and delayed marriage, along with a decrease in fertility rates and ability to spend time with loved ones due to delayed retirement, may also play significant roles (14,19,(21)(22)(23)(24)(25)(26).In the early 2020s, the COVID pandemic increased social isolation for all, which likely increased prevalence of loneliness among older adults.A search conducted in August 2020 yielded 6,901 records, and another 24 records were identified through citation chasing.Of the 6,925 total records, titles of 6,705 clearly indicated that they were not relevant to this review and were eliminated.The abstracts of the 220 remaining records were screened, and 193 more were excluded.The remaining 27 reviews were read in full.Eight of these held incomplete information or failed to include explicit measures for loneliness.Thus, 19 systematic reviews were included.These encompassed 212 primary research studies, of which 101 (47%) were unique (Figure 1).
Only three of the reviews limited their study to articles expressly testing intervention impact on loneliness (17, 56, 60), while the other 16 reviews included a subset of articles testing an intervention's impact on loneliness.For example, Elias et al. reviewed eight articles testing the impact of group reminiscence therapy on alleviating depression, anxiety, and loneliness, with only one article targeting loneliness as an outcome (58).
Characteristics of the 101 primary studies (including only one of the eight in the Elias et al. review) are shown in Table 2.About half (52) of the 101 primary studies were published after 2010.While 69 (68%) of the articles were included in only one of the 19 review articles, 42 were included in two or more of the review articles.Overall, studies sampled populations from 21 nations (Figure 2); including 35 in Europe and the United Kingdom, 34 in the United States, 14 in Asia, 11 in Australia/New Zealand, five in Middle Eastern countries, and three in Canada.2. In terms of intervention objectives, only 10 of the 101 studies had a single objective, while 50 had two, 28 had 3, and 13 aimed to target all 4 areas.Thus, 91 of the 101 studies had an objective to enhance social support, 91 aimed to increase social opportunities, 46 strove to improve social skills, and 18 were designed to change maladaptive social cognition.
In terms of intervention type, 39 of the 101 studies tested interventions offering leisure or skill-building activities, 17 evaluated psychological therapies, 17 tested social facilitation interventions, 14 evaluated health promotion interventions, eight (8%) gaged animalassisted interventions, and six (6%) assessed multi-category programs.While 88% of the psychological therapies and 67% of the multicategory interventions had three or more intervention objectives (e.g., to enhance social support, improve social skills and change maladaptive behavior), health promotion programs and leisure and skill-building activities tended to have fewer intervention objectives.(8,41) and at least one general review found the converse (70).

Effectiveness
Six (75%) of eight general reviews obtained mixed results, while one (13%) concluded interventions to be mostly effective (30), and one (13%) avoided a conclusion due to insufficient evidence (73).Regarding reviews appraising technological interventions, five (71%) of seven reviews summarized this type to be mostly effective, while one (14%) review found mixed efficacy for some assistive technology interventions such as social networking services (11), and one (14%) review could not provide a conclusive evaluation due to the limitations of underlying studies (47).Reviews focused on physical and mental health promotions stated ambiguous results of their effectiveness: one (25%) of four reviews provided evidence that group reminiscence therapy approaches are effective (78), while two (50%) reviews found no overarching proof of programmatic efficacy (67,79).One (25%) review by Cattan et al. relayed assorted results of interventions combatting loneliness (8).
Regarding intervention objective, researchers found 14 (78%) of 18 interventions focused on changing maladaptive social cognition, 31 (67%) of 46 on improving social skills, 59 (65%) of 91 on enhancing social support, and 57 (63%) of 91 on increasing social opportunities to be effective or partially effective.Five (50%) of 10 of uni-objective intervention, 32 (64%) of 50 bi-objective interventions, 16 (57%) of 28 of tri-objective interventions, and 11 (85%) of 13 complete, quadobjective studies were effective or partially effective.Frontiers in Public Health 13 frontiersin.orgmoderate-high quality.These reviews displayed a minimal risk of bias.Two reviews (11%) were assessed as of moderate quality, and one (5%) was deemed low-moderate quality.Every health promotion review was high-quality.In contrast, only two (29%) of seven reviews appraising technology-based interventions and two (25%) of eight general intervention reviews were of high quality.

Quality
In accordance with the AMSTAR 2 guidelines (53), the authors accounted for the following three criteria when developing a summary of review quality.No reviews fully disclosed information regarding primary study funding per Item 10.Most reviews failed to provide a comprehensive list of excluded studies per Item 7.Only 24 studies (24%) employed randomized controlled trial (RCT) designs.Only two studies provided a meta-analysis (67,68); hence, these were the only ones subject to Items 11,12,and 15.Table 2 also lists quality assessment, including grading criteria, for each of the 101 studies within the 19 reviews.The authors found only eight (8%) of the 101 studies to be of high quality (58,82,84,91,98,105,108,161).Eight (8%) were between medium and high quality, 42 (42%) were of medium quality, 20 (20%) between low and medium quality, and 23 (23%) were of low quality.High-quality investigations were rare across intervention objectives, e.g., only two (4%) of 46 intervention that aimed to improve social skills, 7 (8%) of 91 interventions that aimed to enhance social support, 8 (9%) of the 91 that aimed to increase social opportunities, and 3 (17%) of 18 that aimed to change maladaptive social cognition to be of high quality.
Additionally, Table 2 lists the efficacy of each intervention, as noted by the reviews and studies themselves.Of the 101 underlying studies, primary investigators concluded 64 (63%) to be effective or partially effective.However, this varied by study designs, e.g., only 12 of the 24 programs tested through RCT were found to be effective.Irrespective of study methodology, all eight (100%) animal-assisted interventions, five (83%) of six multi-category programs, 13 (76%) of 17 psychological therapies, 26 (67%) of 39 leisure or skill-building activities, 6 (43%) of 14 health promotions, and 6 (35%) of 17 social facilitations were effective or partially effective.

Discussion
To the authors' knowledge, this is the first systematic review of reviews of interventions to combat loneliness in older people.Nineteen systematic reviews amassed the findings of 101 unique studies of interventions.While 42% of the reviews were of the highest quality and contained minimal risk of bias, only 8% of primary studies were of the highest quality according to reviewers.
Regarding usefulness, the authors deducted that 63% of all interventions were effective or possibly effective at combatting loneliness.Multi-category interventions were above-par, along with programs featuring reminiscence therapies (88, 92, 93) and Mindfulness-Based Stress Reduction (96).All animal-assisted approaches were efficacious in combatting loneliness, including living (64,65,100,102,103), robotic (63,101,102), and virtual pet companionship (62).In addition, key findings support interventions with multiple objectives, as 85% of interventions with four objectives (improving social skills, enhancing social support, increasing social opportunities, and changing maladaptive social cognition) alleviated loneliness.The most successful single-objective interventions were those targeting maladaptive social cognition (55-57, 59, 60, 66, 81, 82, 84, 88, 92, 93, 96, 98), presumably to help lonely older adults develop more stable interpersonal relationships and perpetuate social opportunities.This finding is consistent with the hallmark metaanalysis by Masi et al. (35) on subjects of any age.

Limitations
Various considerations tempered the conclusions of this research.First, the authors limited the search to the pre-COVID years.Second, the included systematic reviews had differing foci and scopes, and this heterogeneity hindered comparisons across reviews.Many systematic reviews included were of moderate-high and high quality, but some displayed an elevated risk of bias (72,75).Likewise, many of the studies testing a single intervention exhibited moderate-to-high risk of bias as a product of poor study design.
This systematic review of reviews compiled studies that utilized a variety of loneliness-related outcome measures.While some (i.e., UCLA Loneliness Scale, De Jong Gierveld Loneliness Scale) were welltested with older people and psychometrically sound (61,(167)(168)(169), others were single-item measures or instruments of disputed reliability and validity (8).Also, this review provided a dichotomous summary statistic of effectiveness in its analyses, which reduced complex findings into manageable figures for easy comparison.Binning of interventions by intervention objective is a highly subjective task.Scholars should exercise caution when reducing constructs as complex as loneliness and social isolation into crude metrics, especially together, at the risk of misinterpreting primary study authors' conclusions (29,170).

Recommendations
Three findings stand out.First, allied health professions should develop broad interventions.A multi-objective approach aptly targets the multi-dimensional issue of loneliness (69,76,171,172).Some participants of such interventions may find certain components useful, while other participants would find distinct parts worthwhile.Increasing the number of strategies can target the widest range of participants.This explains the above-average effectiveness ratings of integrated approaches to combating loneliness.The Dutch Geriatric Intervention Program (82) and Finnish psychosocial group rehabilitation intervention (59) are illustrative of this approach.Conclusions here are consistent with the best practices of robust health promotion initiatives targeting a variety of outcomes (173,174).
Second, interventions should become more purpose-driven (67, 71) to stem the losses of identity many lonely older adults feel (78,175).Shvedko et al. remarked that the theory of active engagement explains loneliness reduction through a productive lifestyle that generates a sense of purpose (67,176).Effective programs provide more than aimless social opportunities (30,132), and more than friendly health and social care visitations, as Cattan et al. found (8).Prime examples of purpose-driven approaches are horticulturelearning experiences (60, 149, 155) and fitness-improving "exergames" (144,145,161).The authors also observed specific, purposeful technology trainings to be effective in reducing loneliness, including programs utilizing mobile phones (135), electronic pen pals (163), and videoconferencing software (147, 151, 152).Third, specific types of interventions proved to be more promising than others.Psychotherapeutic interventions utilized the highly effective strategy of modifying maladaptive social cognitionspecifically engaging the theoretical mechanism of action noted by Cacioppo and others (5,15).Animal-assisted interventions were helpful in providing purpose, delivering skills training, and increasing social opportunities for older people (62-65, 100-103), a finding that Banks et al. consistently espoused (65, 102, 103).Finally, technological interventions exhibited potential even as multiple reviews found inconclusive evidence (11,47,149).Chen et al. wrote "the older adults employment of [ICT] reduces their social isolation through the following mechanisms: connecting to the outside world, gaining social support, engaging in activities of interest, and boosting selfconfidence" (76).Simple interventions, with little-to-no expert training or sharing were not effective (71), but approaches that demonstrated technology as a tool to encourage mobility, communication, or education exhibited high value (68,74,177).
Further studies of interventions to combat loneliness are needed.The authors request more individual or cluster RCTs to ensure a highquality body of primary research not limited by risks of bias.Research scientists should heed the differences between social isolation and loneliness, lest phenomenological conclusions become confounded.Lastly, the authors concur with others who note plausible cultural moderators of intervention efficacy (8,30,40,74,75,77) and encourage further examination of culture in perceptions of loneliness and ways to combat it.

Conclusion
The COVID-19 pandemic and associated quarantine orders further exacerbated the loneliness faced by many older adults (178).As health policies combatting loneliness quickly develop-like the national effort in the United Kingdom (179)(180)(181) or the health service company-led strategies in the United States (182-185)-researchers must begin to decipher years of equivocal findings and offer actionable recommendations.This report's value lies in being the first systematic overview of the evidence base on loneliness interventions targeting older people in an attempt to help answer the question "What does an effective intervention look like?"Our findings suggest that interventions utilizing multiple strategies while incorporating purposeful activities are vital in disrupting loneliness and its deleterious effects in older adults.

FIGURE 1 PRISMA
FIGURE 1 PRISMA flowchart of screening and selection.
Studies tested interventions using assorted designs, including controlled trial, clustered controlled trial, quasi-experimental design, pre-experimental (before-and-after) design, cross-sectional, and mixed-method types.Samples ranged from 3 to 5,203 subjects.Interventions occurred in residential care facilities, community day centers, and private homes.While some subjects were as young as 52 years old, the mean age of subjects in each study was above 60 years.Only some studies disclosed full gender characteristics.Six different measures were used across the 101 studies to measure loneliness.Intervention types per Gardiner et al. (first column), activities (fifth column), and objectives per Masi et al. (last four columns) also are shown in Table

FIGURE 2
FIGURE 2Geographic distribution of primary studies.

TABLE 1
Review summary.
Ref., Reference; AOKLS, Ando Osada and Kodama Loneliness Scale; dJG, De Jong Gierveld Loneliness Scale; PGCMS, Philadelphia Geriatric Center Morale Scale, Lonely Dissatisfaction Subscale; SELSA, Social and Emotional Loneliness Scale for Adults; UCLA LS, University of California Los Angeles Loneliness Scale; Victor, Victor single-item scale.

Table 1
recaps included systematic reviews.Review authors gaged interventions to be mostly of mixed effectiveness when aiming to reduce loneliness in older persons.Most reviews found some support for both group and individual-targeted interventions; however, at least one general and one health intervention review found group interventions to be more effective

TABLE 3
Review quality per AMSTAR 2 guidelines.